Ongseong

This extended outer work is placed around the front of a gate for added protection. Invaders have to penetrate the ongseong to reach the gate, and defenders on top of the wall are able to fire down on the intruders from three directions.
Namhan Mountain Fortress has five ongseong in total, three on the South Wall, one on the East Wall (Yeonjubong Ongseong) and one on the North Wall (Janggyeongsasinji Ongseong).